Automatic volume control



Patented Sept. 5, 1939 AUTOMATIC VOLUNIE CONTROL Erich Zepler, Berlin, Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphic m. b. H., Berlin, Germany, a corporation of Germany Application February 4, 1936, Serial No. 62,248 In Germany February 11, 1935 3 Claims. (Cl. 250-20) The present invention is concerned with means adapted to insure automatic volume control in which the transmission efficiency of coupling means is varied as a function of the incoming carrier wave.

Contradistinct from most of the automatic volume control means known in the prior art, in which shift of the working point of one or more amplifier tubes in dependence upon the carrier wave results in a change in the gain, the method here disclosed offers the advantage that the amplifier tubes Work always upon the straight part of their characteristic, and that the risk of causing distortions inherent in a shift of the working point into curved portions of the characteristic is avoided.

Arrangements are known from the earlier art in which a change in the transmission efficiency of the coupling means takes place. In these arrangements the plate-cathode path of an electron tube is connected in parallel relation to an oscillation circuit serving for coupling, while upon the control grid a potential is impressed which is a function of the incoming carrier wave. This potential '5 suitably produced by the plate direct current resulting from the rectification, and the same alters the internal resistance in such a way that by the more or less appreciable damping of the oscillatory circuit which is incidentally occasioned, automatic volume control is obtained.

Now, according to my present invention, the identical aim is attainable with less expenditure in circuit elements by that in one or more coupling means a resistance is provided which is 5 traversed by the direct current of a rectifier tube,

and which changes in value as a function of the size of the said direct current. The said resistance may either be a damping resistance contained in the oscillatory circuit serving for coup ling, or else it may form part of a voltage divider arrangement serving for coupling. The variable resistance could consist, for example, of an iron-hydrogen resistance, or else of a carborundum resistance.

The present invention shall be explained by reference to the drawing which illustrates an exemplified embodiment of the basic concept of the invention. l is the R. F. input tube which is coupled, optionally by way of additional R. F.

;o amplifier stages or else a mixer tube and an I. F. amplifier stage, with the demodulator 2. 3 is the input circuit comprising the coil L, tuner condenser C and the regulating resistance R. This oscillatory circuit is coupled by way of condenser 55 4 with the antenna 5, and by way of condensers 6 and I with the grid and the filament, respectively, of the amplifier tube I. The resistance R is united with the ends of coil L and condenser C being grounded for R. F. The resistance is in unilateral (single pole) connection with the posi- 6 tive terminal of a current source B (not shown), while, by way of the other end, it is associated with the plate of tube 2 through a wire 8, a filter section 9, and the A. F. load resistance H1. The grid of tube I is connected to the grounded end 10 of the grid bias resistor [2 through a radio frequency choke coil H.

Now, if strong signals come in, the direct current of the rectifier tube 2 will change, and thus, also, the size of the resistance R, with the result that the circuit 3 is more strongly damped and that regulation of fading is obtained. If the resistance presents a characteristic curve which falls with growth of the current, then a rectifier of the grid-detection type should be used in which, as known, the plate current decreases with growth of the R. F. potential. Using for the resistance R, for instance, an iron-hydrogen resistance whose resistance value grows also with growth of the current, then the demodulator would have to be of the plate-current detection type, as shown in the drawing, or else a diode.

By means of an arrangement of the kind here disclosed it is possible to handle, also, in the first grid relatively larger radio frequency amplitudes than has been possible in the methods heretofore most generally used in which the amplification of the tubes is altered.

What is claimed is:

1. In a signal receiving system, a tube having input and output electrodes, a tunable signal circuit connected between the input electrodes, a signal output network coupled to the output electrodes, a signal detector having a signal input circuit and an audio output circuit, an element having a non-linear resistance characteristic connected in circuit in said tunable circuit, and said element being included in the detector space current circuit whereby variations in the detector space current caused by signal amplitude variation produce corresponding current variations through said element and regulate the damping of said tunable circuit.

2, In a signal receiving system, a tube having input and output electrodes, a tunable signal cir- 5 cuit connected between the input electrodes, a signal output network coupled to the output electrodes, a signal detector having a signal input circuit and an audio output circuit, an element having a non-linear resistance characteristic connected in circuit in said tunable circuit, said element being of the iron-hydrogen type, and said element being included in the detector space current circuit whereby variations in the detector space current caused by signal amplitude variation produce corresponding current variations through said element and regulate the damping of said tunable circuit.

3. In a signal receiving system, a tube having input and output electrodes, a tunable signal circuit connected between the input electrodes, a signal output network coupled to the output electrodes, a signal detector having a signal input circuit and an audio output circuit, an element having a non-linear resistance characteristic connected in series circuit in said tunable circuit, and said element being included in the detector space current circuit whereby variations in the detector space current caused by signal amplitude variation produce corresponding current variations through said element and regulate the damping of said tunable circuit.

ERICH ZEPLER. 

